Apparatus for determining crystalization temperature

ABSTRACT

Method and apparatus for automatically determining the crystallization temperature of a flowing liquid. Temperature control means are adapted to vary the liquid viscosity within a crystallization zone. Changes in flow or pressure drop caused by the viscosity changes provide the basis for temperature control. Because operation of the system is cyclic, the effects of heat of crystallization of the liquid can be observed on a recording of crystallization zone temperature, thus identifying the crystallization temperature.

United States Patent {72] inventors Joseph Bertoglio Collinsville, Ill.;

Philip L. Deming, St. Louis, Mo.; Joyce G. Eckert, Columbia, IlL; JamesR. Shaier,

Appl. No. Filed Patented Assignee St. Louis, Mo.

APPARATUS FOR DETERMINING CRYSTALIZATION TEMPERATURE [56] ReferencesCited UNITED STATES PATENTS 2,885,885 5/1959 Lupfer et al. 73/172,997,874 8/1961 Billuris et al. 73/17X 3,143,876 8/1964 Wallgren 73/17ABSTRACT: Method and apparatus for automatically deter mining thecrystallization temperature of a flowing liquid.- Temperature controlmeans are adapted to vary the liquid viscosity within a crystallizationzone. Changes in flow or pressure drop caused by the viscosity changesprovide the basis for 6 chumsz Drawmg temperature control. Becauseoperation of the system is U.S. Cl 73/17 cyclic, the effects of heat ofcrystallization of the liquid can be Int. Cl. .I observed on a recordingof crystallization zone temperature,

Field of Search 73/17 thus identifying the crystallization temperature.

I 6 IS A M A G N E T l C FLOWMETER 2 6 l O S T E A M O R V 2 5 R E F RIG E R A N T F ROC E55 24 V SIRE A M T O T R ACI N 6 THERMOCOUPLE 27 CON N ECT ED TO R E CO R D E R M AG N ET l C FLOWMETER l Patented I May 4,1971 in MAGNETIC FLOWMETER f 3 26 lo STEAM OR 25 'REFRlC-ERANT PROCESS24 V SREAM TO TRACING XTHERMOCOUPLE 27 CONNECTED TO RECORDER MAGNETICFLOWMETER I FIGURE 1 U IINFLECTION POINT (28) O m MAXIMUMTEMPERATURE(29) I! D F m U Q.

E E MINIMUM TEMPERATURE 30 T|ME INVENTORS JO EPH BERTOG IO FIGURE 2 5 Lm PHILIP L. DEMING JOYCE G. ECKERT JAMES R.SHAFER ATTORNEY APPARATUS FORDETERMINING CRYSTALIZATION TEMPERATURE material from solution. Themechanism of this process is very complex because it involves thephenomena of diffusion, forplace simultaneously.

A pure liquid on being cooled experiences a decrease in the averagetranslational energy of its molecules, hence its temperature drops untilthe freezing point is reached. At the freezing temperature theattractive forces of the molecules are sufficient to overcome thetranslational energy, and the molecules are forced to arrange themselvesin a geometric pattern which is characteristic for each substance. Whencrystallization begins, heat is evolved in an amount equal to thedifference in heat content between solid and liquid, this.

difierence being'termed the heat of crystallization. This heat evolutionarrests further temperature drop and the temperature of the mixture ofsolid and liquid remains constant as long as both phases are present.Further removal of heat merely results in the crystallization of moreliquid, until finally the whole mass solidifies. Only then does thetemperature begin to fall again on cooling.

The freezing temperature, or the temperature at which solid and liquidare in equilibrium, is constant and definite for each substance. Thistemperature has proven very useful in the chemical arts as an indicatorof certain physical properties. For example, the freezing temperature ofa chemical compound is commonly employed to determine the purity of thatcompound. The freezing temperature is also useful to determineconcentration of a chemical compound within a solution.

The crystallization temperature of a substance is quantitatively thesame as the freezing temperature. Crystallization is usually initiatedby the formation of crystal nuclei within the liquid around which thecrystals grow and .develop. Most liquids have a tendency to supercool,i.e., to be cooled below the freezing temperature, before visiblecrystal formation sets in. This is especially true when the cooling israpid. When optical means are employed to visually determine the onsetof crystallization, therefore, an erroneous reading of freezingtemperature may result. To prevent supercooling and to facilitate theformation of nuclei for crystallization temperature determinationthrough optical detection, it is usually advantageous to cool the liquidslowly, stir vigorously, and seed the liquid. Seeding involves theaddition of a small quantity of the crystals to be formed to act asnuclei. Once crystallization starts, the mass will return to itsequilibrium temperature and remain there until crystallization iscomplete.

When a chemical compound or solution is flowing within a process stream,difficulties arise in the sampling of the stream for determination ofcrystallization temperature. Mechanical problems and problems ofaccuracy often make it impractical, if not impossible, to automaticallymonitor the crystallization temperature of a flowing compound orsolution. High pressures and high temperatures within a process streampreclude the use of conventional instrumentation in many situations.

-mation of nuclei, and crystal growth, all of which can take Certainchemical solutions exhibit a sharp increase in viscosity at'thecrystallization temperature. One example is an aqueous solution ofsodium benzene sulfonate which is formed as a step in the caustic fusionprocess for the manufacture of phenol. Although numerous viscositymeasuring procedures are known to the art, these are not adaptable toall chemical processes. For example, the pressure evaporation of thesodiurn benzene sulfonate solution in the phenol manufacturing processis accomplished under a system pressure of 85 to 95 p.s.i.g. and asolution temperature of approximately 180 C. Conventional viscosityequipment is usually not adaptable to such high pressures andtemperatures. Consequently, crystallization temperature determinationsbased upon viscosity changes cannot be readily determined under suchcomplex conditions.

Another problem which arises with the sodium benzene sulfonate solutionexemplified above concerns the narrow spread between the crystallizationtemperature and the boiling point of the solution, which varies withinthe range of 10 C. to 15 C. The attendant control requirements areextraordinarily difficult.

Prior to the outstanding contributions of the present invention, arandom sampling system was necessarily employed in determining thecrystallization temperature of an aqueous solution such as the sodiumbenzene sulfonate solution exemplified above. The disadvantages of arandom sampling system are numerous. For example, important time is'lostin transferring a sample from a process stream tap to the laboratory fordetermination of crystallization temperature. Errors are oftenintroduced during handling and during exposure to impurities andcontamination. The level of quality control is less than optimum becauseof the practical limit in the number of samplings which can be made.Ideally, therefore, a continuous and automatic determination ofcrystallization temperature within the process stream is needed forproduction operations. The disadvantages of a random sampling system areusually reflected in diminished yield from the chemical process.

The present invention provides a method and an apparatus forautomatically following and recording the crystallization temperature ofa process stream. Broadly stated, the system comprises a crystallizationzone wherein the temperature is controlled by sensing the effects ofviscosity changes in that zone. Operation of the system is cyclic, thusallowing the effects of heat of crystallization to be detected from arecording of crystallization zone temperature. The facility herein fordetecting effects of heat of crystallization assures the accuracy ofcrystallization temperature determinations. There is no Because of theautomatic measurement difficulties recited I above, crystallizationtemperature in a process stream is usually measured on a batch basis byrandom sampling. Many solutions, upon cooling, reach a point at whichone component crystallizes. Determination of the concentration of thiscomponent can be made in the laboratory on a drawn sample reliance onvisual detection of crystal formation and the effects of supercoolingare inconsequential to the effectiveness of the measuring system of thepresent invention.

it is an object of the present invention, therefore, to provide a novelmeans and method of automatically tracking the crystallizationtemperature in a process stream for determination of concentration,purity, and the like.

Another object of the present invention is to provide a temperaturecontrolled crystallization zone responsive to viscosity changes in thefluid flowing therethrough and wherein the heat of crystallization canbe detected.

A further object of this invention is to overcome the inaccuracies anddifficulties inherent in a random sampling system for determination ofcrystallization temperature.

Still another object of the present invention is to provide acrystallization temperature monitor having outstanding repeatability.

Yet another object of the present invention is to provide acrystallization temperature monitor which is readily adaptable toautomatic control.

Other aspects, objects and advantages of this invention will be apparentfrom a consideration of the accompanying disclosure and drawing, andfrom the appended claims.

3 In the Drawing pump 11 which is disposed within line 10. Sidestreamflow to the crystallization temperature apparatus is introduced throughinlet line 12 and is permitted to flow through measuring line 13 andbypass line 14. The division of flow between lines 13 and 14 isdependent upon the setting of bypass valve 15 which is disposed inbypass line 14. Valve 15 affords vemier control of the flow through thecrystallization zone, i.e., through line 13. Isolation valves 16 and 17are disposed in line 13 to permit shutoff of the crystallization zonewhen so required.

With continued reference to FIG. 1, that portion of sidestream flowwhich enters line 13 passes through magnetic flowmeter 18, a devicewhich generates an electrical signal proportional to the rate of fluidflowing therethrough. After discharging from flowmeter 18, thesidestream flow is directed through a coil of process tubing identifiedby reference numeral 19, and is then directed through outlet line 20 byway of magnetic flowmeter 21 and system control valve 22 on its returnto the process stream. Valve 22 affords control of the overallsidestream flow rate. This control is accomplished automatically bycoordinating the output signal from magnetic flowmeter 21 withcontroller 23 of valve 22.

Again refen-ing to FIG. 1 of the drawing, it will be observed that aheat transfer fluid such assteam or a refrigerant is introduced to thecrystallization zone through control valve 24 and tracing supply line 25to afford temperature regulation. Where the process stream fluid is anaqueous solution of sodium benzene sulfonate, steam is an effective heattransfer medium. Steam tracing, for example in the form of coppertubing, is brazed not only to the process tubing of coil 19, but also tothe sections of tubing upstream and downstream of coil 19. Steam tracingfor flowmeter 18 is provided by a copper or stainless steel tubedisposed concentrically with respect to the flow passage through theflowmeter. Control valve 24, therefore, regulates the quantity of steamadmitted to tracing supply line 25, and accordingly, to coil 19. Thesetting of control valve 24 is determined by the electrical signal fromflowmeter 18. This signal is coordinated with controller mechanism 26 ofvalve 24.

Operation of the crystallization temperature system illustratedschematically in FIG. I is described as follows. Process stream liquidfrom line 10 is diverted to the measuring apparatus through inlet line12. The rate of sidestream flow is determined by control valve 22 whichis responsive to the programmed output signal of flowmeter 21 in thedischarge section of the apparatus. In the sodium benzene sulfonatesolution exemplified herein. a sidestream flow rate of 0.5 gallons perminute is satisfactory. With little or no steam applied to the tracingon coil 19, the test solution flowing in line 13 approaches the viscousstage, thus reducing the rate of flow. The

output signal from flowmeter I8 is thereby reduced in its communicationwith steam control valve 24. The set point on controller 26 of valve 24is preadjusted to a determined setting, e.g., 0.3 gallons per minute.Thus, when the flow rate through coil 19 decreases to 0.3 gallons perminute because of increased viscosity, steam valve 24 is automaticallycaused to move to the fully opened position. The test solution hasreached a slushy condition but the rapid introduction of steam 'to thetracing quickly decreases the test solution viscosity.

1 'Ihereupon, the flow rate is restored to the initial rate of 0.5

4 gallons per minute. When the initial rate is restored, the outputsignal from flowmeter 18 causes control valve 24 to go fully closed,thus shutting off steam to the tracings. A measuring cycle is thereuponcompleted.

Control of the apparatus of FIG. 1 is such as to allow the test solutionto reach the crystallization temperature in coil 19 without causing theflow to stop. Thermocouple 27 is affixed to the tar tracing on thedownstream or coolest part of coil 19 and is electrically connected to arecording device such as a recording potentiometer. Thus, a continuousrecording of solution temperature in the measuring zone is available tothe process operator.

FIG. 2 of the drawing illustrates a typical portion of a continuoustemperature recording obtained during crystallization temperaturemeasurements of an aqueous solution of sodium benzene sulfonate. Thisrecording was obtained from the apparatus of the present invention ashereinbefore described. Visual inspection of this recording provides tothe operator the necessary information for rapid determination ofcrystallization temperature. This is illustrated by reference to FIG. 2wherein the inflection points on the recording illustrated typically byreference numeral 28 signify a temperature change caused by the heat ofcrystallization. As hereinbefore stated, the ability to detect the heatof crystallization provides an immediate indication of crystallizationtemperature. Thus, a process operator, by merely reading the temperaturescale at the inflection point 28, has a direct measurement ofcrystallization temperature. The maximum temperature points typified byreference numeral 29 are irrelevant herein to the measurement ofcrystallization temperature. These peaks represent temperature overshootin the system when steam is cut off from the tracing of coil 19 duringeach cycle. Similarly, the minimum temperature points on the recordingof FIG. 2, illustrated typically by reference numeral 30, arecharacteristic of the system when steam is introduced to the tracing ofcoil 19 during the cycle.

With further reference to FIG. 2 of the drawing, it can be observed thatthe numerical value of crystallization temperature of the sodium benzenesulfonate solution is approximately C. while the maximum and minimumtemperatures are about C. and l65 C., respectively. The temperatureexcursions in the measuring zone, therefore, are relatively minor. Thisis advantageous because the boiling temperature of the solution iswithin 10 C. to l5 C. of the crystallization temperature.

The critical variable being sought in using the method and apparatus ofthe present invention is crystallization temperature. The facility todistinguish the crystallization temperature through automatic recordingmeans is directly attributable to graphic exhibition of the heat ofcrystallization. Because of the heat of crystallization is signified onthe recording by an inflection point in each cycle as illustrated byreference numeral 28 in FIG. 2, the crystallization temperature can beaccurately and rapidly ascertained. Were it not for inflection point 28,the operator would be unable to determine crystallization temperaturewith such a degree of precision in an automatic test system.

In a sodium benzene sulfonate solution such as hereinbefore described,the crystallization temperature data is used as an indication of saltconcentration in the solution. It is further employed to indicate to thesystem operator that the pressure evaporation process is being carriedout at the desired temperature.

In a preferred embodiment of the apparatus illustrated schematically inFIG. 1, coil 19 is made of 98-inch stainless steel tubing having a coildiameter of approximately 9 inches and having 9 coil turns. The steamtracing affixed tangentially to coil '19 can be, for example 'A-inchcopper tubing. At a flow rate of 0.5 gallons per minute in thisembodiment, the residence time of the test solution within coil 19 isapproximately 12 seconds.

It will be readily apparent to those skilled in the art that the meansand method of the present invention have wide applicalization point datahas significance. The present invention is not. restricted to fluidshaving high crystallization points. Where the crystallization point isbelow room temperature,

. for example, the same system would be employed with the exception thatrefrigeration would be applied to the coil tracing to attaincrystallization.

Although the preferred embodiment of the present invention detectsviscosity changes in the measuring zone by observing changes in rate offluid flow, there are other means of detecting viscosity changes. Forexample, an alternate embodiment of the illustrated apparatus whichsenses changes in pressure drop across the coil has been satisfactorilyemployed for measurement of crystallization temperature. An increase inpressure drop indicates that crystallization is proceeding and arecording of temperature will again show crystallization temperature atthe heat of crystallization inflection point. To avoid inadvertentfailure of the viscosity sensing instrumentation due to crystallineformations, however, it is advantageous to introduce steam thereto as inthe preferred embodiment herein.

While this invention has been described with respect to certain specificembodiments, it is not so limited, and it is to be understood thatvariations and modifications thereof may be made without departing fromthe spirit or scope of the following claims.

The embodiments of this invention in which an exclusive property orprivilege is claimed are defined as follows:

We claim:

1. Apparatus for determining the crystallization temperature of aflowing liquid comprising:

a. conduit means adapted to house said flowing liquid;

b. viscosity sensing means responsive to viscosity changes within saidconduit means; c. liquid temperature control means cooperating with saidviscosity sensing means; and d. temperature indicating means adaptedtomonitor crystallization zone temperature. 2. Apparatus for determiningthe crystallization temperature of a flowing liquid comprising:

a. conduit means adapted to house said flowing liquid; b. acrystallization member within said conduit means; c. viscosity sensingmeans responsive to viscosity changes within said crystallizationmember; d. liquid temperature control means cooperating with saidviscosity sensing means; and e. temperature indicating means adapted tomonitor crystallization zone temperature. 3. Apparatus for determiningthe crystallization temperature of a flowing liquid comprising:

a. a sidestream conduit communicating with a process stream; b.sidestream flow control means within said conduit; c. a crystallizationmember within said conduit; d. viscosity sensing means responsive toviscosity changes within said crystallization member; e. liquidtemperature control means cooperating with said viscosity sensing means;and f. temperature indicating means adapted to monitor crystallizationzone temperature. 4. An apparatus of claim 1 wherein the viscositysensing means is a flowmeter.

5. An apparatus of claim 1 wherein the viscosity sensing means is adifferential pressure meter.

6. An apparatus of claim- 2 wherein the crystallization member is a coilof temperature controlled tubing.

2. Apparatus for determining the crystallization temperature of aflowing liquid comprising: a. conduit means adapted to house saidflowing liquid; b. a crystallization member within said conduit means;c. viscosity sensing means responsive to viscosity changes within saidcrystallization member; d. liquid temperature control means cooperatingwith said viscosity sensing means; and e. temperature indicating meansadapted to monitor crystallization zone temperature.
 3. Apparatus fordetermining the crystallization temperature of a flowing liquidcomprising: a. a sidestream conduit communicating with a process stream;b. sidestream flow control means within said conduit; c. acrystallization member within said conduit; d. viscosity sensing meansresponsive to viscosity changes within said crystallization member; e.liquid temperature control means cooperating with said viscosity sensingmeans; and f. temperature indicating means adapted to monitorcrystallization zone temperature.
 4. An apparatus of claim 1 wherein theviscosity sensing means is a flowmeter.
 5. An apparatus of claim 1wherein the viscosity sensing means is a differential pressure meter. 6.An apparatus of claim 2 wherein the crystallization member is a coil oftemperature controlled tubing.